The S-61N is one of two civilian variants of the military SH-3 Sea Knight. It’s a product of the American Sikorsky helicopter company. Along with the S-61L it is the most widely used airliner and offshore oil rig support helicopter.
The S-61N exists thanks to a contract that Sikorsky won from the US Navy in 1957. The navy wanted an amphibious anti-submarine helicopter and Sikorsky won the chance to provide on. This was of course the first Sea King prototype which then became the S-61N under discussion here.
While the Sea King prototype first flew in 1959, it wasn’t until the latter half of 1962 that the S-61N first took flight. The 61N and 61L are virtually identical, but the “N” model is better optimized to operate over water since it still has the amphibious floats of the Sea King.
The very first civil operator of the S-61N was Los Angeles airways, introducing them in March of 1962.
Only 119 “L” an “N” were built and the main users of these helicopters were CHC Helicopters, Bristow Helicopters and AAR Airlift.
The S-61N shares the power plants from the Sea Hawk, namely the civilian version of the T58s found in the military SH-3. These provide 1350 shaft horsepower.
An improvement of the S-61N is the Mk II model. It improves the performance of the original S-61N across the board. Upping the per-engine shaft horsepower to 1500.
Today the S61 lives on as the S-61T Triton. Sikorsky and Carson helicopters made several upgrades including carbon composite rotors, full airframe refurbishment, conversion from folding to non-folding rotors and a modular wiring harness. They also added a new avionics suite. The first helicopters to be converted to Tritons were all S-61Ns. So in a way the S-61N may live on in one form or another for some time yet.